July 15, 2002 - Marlin Mickle wasn't interested in radio frequency identification, or any other form of auto-identification for that matter. As a professor at the University of Pittsburgh's School of Engineering, he was developing automatic remote sensing devices that could operate without batteries or wires and form ad hoc wireless networks. But he may have stumbled onto an approach that could transform radio frequency identification.

The PENI tag

Mickle's work was closely related to RFID. His sensors needed to gather power from the air and transmit information wirelessly, just as RFID tags do. But his sensors required more power than a typical RFID tag could muster, which led him to adopt a novel approach to RFID -- energy harvesting.

Most passive RFID tags – those without a battery to power their circuitry -- gather energy by coupling to the reader's communication field. That is, the coiled reader antenna sends out radio waves. When the waves reach the coiled antenna on the tag, they form an electromagnetic field. The tag draws power from this field.

The tag sends back data passively, usually by a method known as backscatter. Tags that use backscatter take the incoming waveform and reflect back a modulated wave. The modulated wave has to pass through all the energy coming from the reader, so the reader has to be very sensitive to pick it up. The system is inefficient. It would be like one boat communicating by flashing a light, and a second boat responding by using a mirror to reflect back what little light hits the mirror.